A system has been developed which determines the consciousness-degraded state of the driver of the vehicle due to, for example, fatigue, drowsiness, and inattentive driving and outputs a warning to the driver. As a method for determining the consciousness-degraded state, for example, there is a method which detects, as an abnormal behavior, a unique steering pattern that appears in the consciousness-degraded state. Patent Literature 1 discloses a technique which detects the speed of the vehicle or a steering angle, determines that the driver has fallen asleep at the wheel when sudden steering is detected after a non-steering state is maintained for a predetermined period of time and the steering pattern belongs to a reference pattern, and operates a warning generation device.